The best way for me is to select the faces in poly-mode which are relevant to the jacket. Then detach them as an object. After that scale them a little bit up for extrusion or the “soldify”-modifier. Push the vertices in Place, cut, delete and so on like all the other boxmodels.
Here in your case u can do this way with the shoulders etc…
Then you can extrude the lower edges to create the bottom part of the jacket.
The cape could be extruded from a spline. After that extrude the faces for the thickness.
Hope it works…:shrug: 
cya






